Khalid Sheikh Mohammed

Mohammed is an American-educated Pakistani. The US claims he masterminded the September 11 attacks. He was subjected to "waterboarding" during questioning and confessed to roles in 30 plots other than 9/11, including planned attacks on Big Ben and Heathrow airport, and beheading of Wall Street Journal reporter Daniel Pearl in Pakistan, according to transcripts at Guantánamo Bay. Mohammed was believed to be al-Qaida's third most senior member when he was arrested in Rawalpindi in March 2003.

Ramzi bin al-Shibh

Shibh is a Yemeni national who at one stage lived with September 11 ringleader Mohammed Atta. Shibh, allegedly the main intermediary between hijackers and al-Qaida leaders, has been described by officials as a "key facilitator" and "lead operative" in a plan to crash hijacked airliners at Heathrow. In an interview with an al-Jazeera reporter in 2002, he showed souvenirs of the 9/11 planning, including a flight instruction manual signed by Atta.

Ali Abd al-Aziz Ali

Ali, also known as Ammar al-Baluchi, is a nephew of Khalid Sheikh Mohammed and a cousin of the jailed 1993 World Trade Centre bomber Ramzi Youssef. He stands accused of being Mohammed's 9/11 lieutenant. US intelligence officials allege Ali delivered funds to the 9/11 hijackers and later helped Mohammed to communicate with Richard Reid, the shoe bomber serving life in a US jail for plotting to kill 198 people on a transatlantic flight in 2001.

Mustafa Ahmed al-Hawsawi

Allegedly Ali's assistant, he has also been accused of being an al-Qaida paymaster. Financial links have been found between Hawsawi, other terror suspects and some 9/11 hijackers, US intelligence claims.

Walid bin Attash

Attash, known as Khallad, is a Yemeni raised in Saudi Arabia. He was allegedly selected as a hijacker, but was prevented from taking part when he was briefly arrested in Yemen in 2001. He is said to have served as Osama bin Laden's bodyguard. The Pentagon says he admitted masterminding the bombing of destroyer USS Cole in Yemen in 2000, which killed 17 US sailors. Attash also said he helped to plan the 1998 bomb attacks on US embassies in Kenya and Tanzania that killed 213 people.